1. Field of the Invention
The present invention relates to an optical component, and more particularly to a wavelength division multiplexed (WDM) coupler.
2. Description of the Prior Art
In optical fiber technology, wavelength division multiplexed (WDM) couplers are used to combine or separate optical signals with different wavelengths. As the WDM couplers are being more broadly applied in the telecommunications, data communications and CATV industries, the fiber optic component industry is now confronted with increasing requirements for WDM couplers with high performance and reliability.
FIGS. 1(a) and 1(b) respectively show the optical paths of a WDM coupler. Referring to FIG 1(a), light beams with wavelengths λ1, λ2 are transmitted through an optical fiber 1 of an optical ferrule 3, and are transmitted to a GRIN lens 4, parallel light beams are passed from the GRIN lens 4 through an optical filter 5, and the reflective light beams with wavelength λ2 are reflected by the optical filter 5 and are transmitted back through the GRIN lens 4 and are coupled into an optical fiber 2. Light beams with wavelength λ1 are transmitted through the optical filter 5, and transmitted to a GRIN lens 6 and coupled into an optical fiber 8 of an optical ferrule 7. Referring to FIG. 1(b), since light beams can be reversed, if light beams with wavelength λ2 are emitted from the optical fiber 2, and light beams with wavelength λ1 are emitted from the optical fiber 8, the optical fiber 1 will attain light beams having light beams having wavelengths λ1, λ2.
FIG. 2 shows the structure of a typical WDM coupler fabricated according to packaging technologies based on epoxy bonding or welding. The WDM coupler includes:                (1) a first collimator 10 including a dual fiber pigtail 101, a GRIN lens 102 and a glass tube 104; the dual fiber pigtail 101 being retained in the glass tube 104, and the GRIN lens 102 being adhered to an end surface of the dual fiber pigtail 101 using heat-curing epoxy (not labeled);        (2) an optical filter 103 attached to the GRIN lens 102 using heat-curing epoxy (not labeled);        (3) a first sleeve 106 coated with gold and retaining the first collimator 10;        (4) a second collimator 20 including a single fiber pigtail 201, a GRIN lens 202 and a glass tube 203, the single fiber pigtail 201 and the GRIN lens 202 being retained in the glass tube 203;        (5) a second sleeve 206 coated with gold and enclosing the second collimator 20; and        (6) an outer sleeve 30; the first and second collimators 10, 20 are respectively soldered in the outer sleeve 30 through apertures 40.        
This WDM coupler has good performance and stability based on soldering technologies. Soldering process must be performed at high temperature, which will causes stresses in the components. To release the stresses must take hours, which lead to long manufacturing procedure. In addition, there is a temperature stability issue. Thus, performance and reliability of the WDM coupler are limited by the above-mentioned difficulties.
Therefore, it is desired to provide a WDM coupler which has excellent stability and low manufacturing cost.